Adjusting mechanism for neck aligner in stringed instrument

Abstract: A mechanism 28 for adjusting the tension in a rod 30 in the neck 21 of a stringed instrument 30 such as a guitar comprises a first member 12 attached to one end 31 of the rod 30 and a second member 11 attached to the body of the instrument. The distance between the first and second members can be adjusted to vary the tension in the rod by means of cam members, comprising chamfered blocks 14 and 15 which co-operate with the first member 12. When the cam members 14,15 are brought together by tightening a screw 16, the first and second members are forced apart. This increases the tension the rod 30 and thus varies the degree of bending of the neck 21. The invention also extends to an instrument comprising such an adjusting mechanism.

Description: The present invention relates to an adjusting mechanism for a neck aligner for use in a stringed instrument. It is known that the necks of stringed instruments are deformed by the tension of the strings which extend over the stringed instrument, in such a way as to draw the head part of the neck towards the side of the instrument bearing the bridge. To counteract this, an aligner is provided in the neck of the stringed instrument to straighten the bending deformation of the neck. This aligner, which comprises a resilient rod member with a high rigidity inserted into the neck as a truss rod, is adapted to apply a straightening force to the instrument to counteract the bending deformation of the neck. The straightening force is generated by reducing the length of the truss rod when bending deformation occurs in the neck. An aligner as described above employing two rod members is disclosed in Japanese Patent Application Disclosure Gazette (TOKUKAI) Nos. JP-A-1 231 098 and JP-A-1 234 898, and an aligner employing one rod member is disclosed in Japanese Patent Application Disclosure Gazette (TOKUKAI) No. JP-A-1 213 697 and Japanese Utility Model Application Disclosure Gazette No. JP-U-333 488. The above-described aligners are each provided with an adjusting mechanism for reducing the length of the truss rod inserted into the neck. The adjusting mechanism is arranged in a hollow space formed in the head part of the neck in the above Japanese Patent Application Disclosure Gazette No. JP-A-1 234 898 and Japanese Utility Model Application Disclosure Gazette No. JP-U-3 33 488, and arranged in the part of the neck which is connected to the body in Japanese Utility Model Application Disclosure Gazette No. JP-U-5 838 192. With these adjusting mechanisms, a user can perform adjustment by directly inserting an adjusting tool to the end of the truss rod, through the hollow space of the head part of the neck or the internal hollow space of the body. However, there are various types of stringed instruments in which an internal hollow space cannot be formed in the body, or the head is not provided with a hollow space to improve the appearance of the neck, for example a "Fender"-type guitar. In this type of stringed instrument, the length of the truss rod cannot be adjusted while the neck is attached to the body using the known adjusting mechanisms. Furthermore, stringed instruments in which the user adjusts the length of the truss rod by inserting a wrench through the hollow space of the head part of the neck or the hollow space formed in the body are disadvantageous, as the range of movement of the wrench is limited by the strings, and adjusting work is difficult as adjustment should preferably be carried out when the instrument is tuned, which necessitates inserting the wrench through tuned strings. An adjusting mechanism which enables the adjustment of the length of the truss rod in the neck from the side of the neck has been proposed, in which a worm gear mechanism is coupled to the end part of the truss rod. This mechanism is disclosed in Japanese Utility Model Application Disclosure Gazette Nos. JP-U-54-94220 and JP-U-3-20392. The adjusting mechanism using the worm gear mechanism is constructed so that a threaded part formed on the end part of the truss rod is meshed with a worm wheel. The worm wheel is rotated by an external operation while meshed with the thread on the truss rod to move the threaded part of the truss rod forwards and backwards parallel to the axis of the worm wheel, thereby changing the length of the truss rod. In the adjusting mechanism described above, there is a problem in that it is necessary for the pitch of the worm wheel to be small in order to accurately adjust the length of the truss rod. However, if the pitch of the worm wheel is made too small, the adjusting mechanism cannot withstand the force applied during adjustment of the length of the truss rod. Moreover, external operation of the worm wheel cannot be carried out lightly and smoothly since the worm wheel is internally meshed with the end part of the truss rod and adjustment of the length of the truss rod is doubly decelerated by the internal and external threads of the worm wheel. According to one aspect of the invention, there is provided an adjusting mechanism for a neck aligner in a stringed instrument, wherein the tension in a rod in the neck of the stringed instrument is varied to compensate for distortions, the adjusting mechanism comprising a first member longitudinally movable with a first end of the rod and a second member adapted to be prevented from longitudinal movement relative to the body of the instrument, and means for effecting longitudinal movement of the first member relative to the second member so as to vary the tension in the rod. In a preferred embodiment, there is provided an adjusting mechanism for a neck aligner in a stringed instrument characterized in that a front block and a rear block opposing to each other in an axial direction of a neck of the stringed instrument are accommodated in an internal chamber formed in a neck base of said stringed instrument, a depressing block and a thread-engaging block are arranged opposing to each other between the right and left ends of the front and rear blocks, said front block and said rear block are respectively provided, at their central parts, with a through hole into which an end part of a truss rod is loosely inserted, a threaded cylinder into which a threaded part formed at the end of said truss rod is meshed is abutted against the rear surface of said rear block, an adjust screw is inserted into a through hole which is provided in the side wall of said internal chamber so that said adjust screw orthogonally intersects said truss rod, said adjust screw is inserted through said depressing block and its extreme end part is threaded and meshed with said thread-engaging block, said adjust screw may be rotated by an external operation outside said through hole and provided with a pushing means for pushing said depressing block toward said thread-engaging block side, a slope which declines rearwardly is formed with the same angle of inclination at both ends of said rear block, respectively, and rear end surfaces of said depressing block and said thread-engaging block which respectively contact the slopes of said rear block are formed as a slope having the same angle of inclination as the slope of said rear block whereby said depressing block and said thread-engaging block may be moved by rotating said adjust screw in a direction where these blocks approach and move away from each other to move said rear block in the axial direction of the neck and thus the length of said truss rod in an elongate groove provided on the neck may be adjusted. The invention also extends to a stringed instrument comprising such an adjusting mechanism. According to a further preferred embodiment, the adjusting mechanism comprises a front block and a rear block facing each other in the axial direction of the neck in an internal chamber formed in a base of the neck. A depressing block and a thread-engaging block are arranged between the right and left ends of these blocks, and an adjust screw passes through a through hole into the internal chamber from the side of the neck, and is inserted into the pair of blocks. The adjust screw is formed to be externally operated. Through holes are formed respectively in the central parts of the front block and the rear block. One end of the truss rod is formed as a threaded part. The rod extends through the pair of blocks and projects beyond the rear block. The threaded part is screwed into an internally-threaded cylinder which abuts the rear surface of the rear block. The adjust screw passes through a bore provided in the depressing block and engages in a threaded hole in the thread-engaging block. In order to move the depressing block when the adjust screw is turned, a depressing pipe having a larger diameter than the bore of the depressing block is provided as a depressing means between the depressing block and the head of the adjust screw. The right and left ends of the block are chamfered to provide surfaces which surfaces are inclined backwards at the same angle to the axis of the neck. The rear surfaces of the thread-engaging block and the depressing block are likewise chamfered to provide surfaces which closely contact the surfaces on the rear block. The rear surface of the front block is formed as a smooth planar surface and the front end surface of the depressing block and the front end surface of the thread-engaging block are formed as smooth planar surfaces. In use of the adjusting mechanism described above, when the adjust screw is turned by means of a tool inserted through the through hole provided at the side of the neck to advance the threaded part of the adjust screw more deeply into the thread-engaging block, the thread-engaging block and the depressing block move in a direction to approach each other, and the rear end surfaces of both blocks push the rear block backwards. Therefore, the rear end of the truss rod which is engaged with the rear block is drawn out from the elongate groove and the tension in the truss rod is increased to increase a resilient force, that is, a straightening force. The variation of tension in the truss rod in the elongate groove is determined by the pitch of the threaded part of the adjust screw and the inclination angle of the slopes of the rear block. An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 shows a perspective view of a guitar provided with an adjusting mechanism according to the present invention; Fig. 2 shows a side view of the neck of the guitar; Fig. 3 shows a bottom view of part of the neck of the guitar; Fig. 4 shows a cross-sectional view along line 4-4 in Fig. 3; Fig. 5 shows an exploded perspective view of the adjusting mechanism according to the present invention; and Fig. 6 shows a schematic view of the adjusting mechanism. Fig. 1 shows a guitar provided with an adjusting mechanism according to the present invention. A bridge 23 is provided on the body 22 of the guitar 20, tuning pegs 24 are mounted on the neck 21, and strings 25 extend between the bridge 23 and the pegs 24. A truss rod 30 is accommodated in an elongate groove 26 provided in the neck 21 and the elongate groove 26 is closed by a fingerboard 27. One end of the truss rod 30 is fixed in the elongate groove 26 and the other end 31 is externally threaded. An internal chamber 28 for accommodating the adjusting mechanism 10 is formed at the base 211 of the neck 21, where the neck 21 is connected to the body 22. A hollow 281 which is open at the bottom of the neck 21 (that is, the side opposite to the surface where the strings 25 extend) communicates with the chamber 28, as does a through hole which is open at the side of the neck 21. The adjusting mechanism 10, as shown in Figs. 3 to 5, comprises a front block 11 through which the said other end of the truss rod 30 extends and which contacts a front wall 283 of internal chamber 28 and a rear block 12 which is opposite the front block 11 through which the said other end of the truss rod 30 also extends. A threaded cylinder 13 is screwed onto the threaded part 31 of the end of truss rod 30, and is in contact with the rear surface of the rear block 12. The cylinder 13 is provided with a receiving part 131 which accepts, for example, a hexagonal wrench to enable screwing and unscrewing. A thread-engaging block 14 and a depression block 15 are provided at right and left positions opposite each other between the front block 11 and the rear block 12. An adjust screw 16 passes through the depressing block 15 and is screwed into the thread-engaging block 14, and a tubular member 17 is externally fitted to the adjust screw 16 and acts as a depressing means. The depressing means can be formed so that the tubular member 17 is integral with the adjust screw 16, and a flange type depressing piece can be formed on the adjust screw 16. The front block 11 has a through hole 111 provided in its central part through which the truss rod 30 passes, and a rear surface 112 facing the rear block 12 which is formed as a smooth planar surface. The rear block 12 is provided with a through hole 121 through which the threaded part 31 of the truss rod 30 passes loosely. Both sides of the front surface of the block 12 facing the front block 11 are formed as smooth planar surfaces 122 and 122'. These surfaces are inclined relative to the axis of the truss rod at the same angle, such that projections of the planar surfaces intersect at the centre of the rod further from the said other end than the position of the first block. The thread-engaging block 14 is provided in its central part with a thread-engaging hole 141 in which the threaded part 161 of the adjust screw 16 intersecting the truss rod 30 engages. The thread-engaging block has a front end surface 142 which contacts the front block 11 and is formed as a smooth planar surface, and a rear end surface 143, which contacts the rear block 12 and is formed as an inclined plane to closely contact the surface 122 of the rear block 12. The depressing block 15 is provided with a through hole 151 in its central part through which the adjust screw 16 passes. It has a front end surface 152 which contacts the front block 11 and is formed as a smooth planar surface, and a rear end surface 153 which contacts the rear block 12 and is formed as an inclined plane to closely contact the surface 122' of the rear block 12. The adjust screw 16 is inserted through the through hole 282 at the side of the internal chamber 28 so that the shank part of the adjust screw 16 passes through the through hole 151 of the depressing block 15. A coupling means such as, for example, a wrench hole 163 for accepting a hexagonal wrench is provided at the head part 162 of the screw, and can be operated by external means. The screw 16 has a threaded front part 161, which engages in the thread-engaging block 14. The depressing block 15 is constructed so as to be urged towards the thread-engaging block 14 by the depressing means provided on the adjust screw 16. In this embodiment a tubular member 17 having a larger diameter than the through hole 151 of the depressing block 15 is provided between the head part 162 of the adjust screw 16 and the depressing block 15. A bore 284 for accommodating the threaded cylinder 13 is provided in the internal chamber 28 of the neck 21, and this bore 284 passes through the base 211 of the neck 21 in the axial direction of the neck 21. The bore has a certain curvature so as to be formed along a curve of the truss rod 30. A blind bore 285, in line with the through hole 141 of the thread-engaging block 14, is provided in the internal side wall of the internal chamber 28 adjacent the thread-engaging block 14 as shown in Fig. 3. The end part of the threaded part 161 of the adjust screw 16, which protrudes from the thread-engaging block 14, is accommodated in the blind bore 285. After assembling the neck 21 with the body 22, the adjust screw 16 is turned to set the thread-engaging block 14 and the depressing block 15 so that these blocks are positioned an intermediate distance from each other. Secondly, the threaded cylinder 13 is rotated by driving the receiving part 131 of the threaded cylinder 13 with a tool such as a wrench, in order to put the truss rod 30 under tension in the elongate groove 26 to compensate for the expected bending deformation of the neck. At this stage, the neck 21 is slightly bent in an opposite direction to the bending deformation caused by the tension of the strings, and the threaded cylinder 13 is forced into contact with the rear block 12. Thus the neck 21 as assembled with the body 22 is bent slightly backwards. The strings 25 are then strung onto the instrument body and tuned. If the neck 21 is bent forwards (as is usual), the adjust screw 16 is turned one way by a wrench and, if it is bent backwards, the adjust screw 16 is turned the other way to adjust the warp of the neck. When the adjust screw 16 is turned the first way as described above, the thread-engaging block 14 is pulled in the direction of arrow a by the adjust screw 16 and the depressing block 15 is pushed out in the direction of arrow b by the tubular member 17, as shown in Fig. 6; the rear block 12 is thus urged in a direction away from the front block 11 and the truss rod 30 in the elongate groove 26 is put under increased tension, which accordingly increases the force tending to straighten the bending of the neck 21. The adjusting mechanism can be used in a neck aligner constructed with an addition rod member in parallel to the truss rod 30. In this case, the additional rod member can be arranged so that one end of the rod member is coupled to the end of the truss rod 30 and the other end thereof is fixed in the elongate groove 26, as in the prior art device. The adjusting mechanism is adapted to move the depressing block 15 and the thread-engaging block 14 towards and away from one another by operation of the adjust screw 16 by means of the external operating means, thereby moving the rear block 12 in the axial direction of the neck 21. The movement of the rear block 12, which determines the tension in the truss rod 30 in the elongate groove 26, can be finely adjusted by reducing the pitch of the threaded part 161 of the adjust screw 16, and, because the amount of movement of the rear block 12 is also affected by the inclinations of surfaces 122 and 122', fine adjustment of the amount of movement can be achieved by selecting the angle of inclination of the surfaces. The adjusting mechanism allows adjustment of the tension in the truss rod 30 by directly turning the adjust screw 16 and therefore provides an effect to facilitate the adjusting work without a possibility of deceleration function, differing from the worm gear. The adjusting mechanism also provides a way of accurately correcting the bending of the neck 21 even after the neck 21 has been assembled with the body 22.

Claims: An adjusting mechanism (28) for a neck aligner in a stringed instrument (20), wherein the tension in a rod (30) in the neck of the stringed instrument is varied to compensate for distortions, the adjusting mechanism comprising a first member (12) longitudinally movable with a first end (31) of the rod and a second member (11) adapted to be prevented from longitudinal movement relative to the body of the instrument, and means (14, 15, 16) for effecting longitudinal movement of the first member (12) relative to the second member (11) so as to vary the tension in the rod. A mechanism as claimed in claim 1, wherein said means for effecting longitudinal movement (14, 15, 16) of the first member (12) relative to the second member (11) comprises cam means. A mechanism as claimed in claim 2, wherein said cam means comprises two cam members (14, 15) arranged such that motion of the cam members towards each other causes motion of the first and second members (12, 11) away from each other. A mechanism as claimed in claim 3, wherein a screw (16) is provided for moving the cam members (14, 15) towards and away from each other, the screw passing through one of the cam members (15) and being threadedly engaged in the other of the cam members (14), whereby rotation of the screw causes motion of the cam members towards and away from each other. A mechanism as claimed in any of claims 2 to 4, wherein the first member (12) and the cam members (14, 15) co-operate by means of mutually contacting surfaces (122, 143; 122', 153) on the first member (12) and the cam members (14, 15), the surfaces being inclined relative to the directions of motion of the first member and the cam members. A mechanism as claimed in claim 5, wherein the second member (11) and the cam members (14, 15) contact each other by means of surfaces (112, 142, 152) arranged perpendicular to the axis of the rod (30). A mechanism as claimed in any preceding claim, wherein said first member (12) and said second member (11) have through holes (111, 121) through which the rod (30) passes. A mechanism as claimed in claim 7, wherein the first end (31) of the rod (30) projecting from the first member (12) is externally threaded, and engages with an internally threaded member (13), one end of which abuts the first member (12). A stringed instrument comprising an adjusting mechanism (28) as claimed in any preceding claim. An instrument as claimed in claim 9, wherein the adjusting mechanism (28) can be accessed from the outside of the instrument (20).

Inventors: OKAMURA MASAKI, OKAMURA, MASAKI
Applicants: GOTOH GUT YUGEN KAISHA
Application year: 1994
Main classification: G10D3
IPC codes: G10D3, G10D1